Phenomenon (\fi-ˈnä-mə-ˌnän, -nən\) :
1. something (such as an interesting fact or event) that can be observed and studied and that typically is unusual or difficult to understand or explain fully.
2. someone or something that is very impressive or popular especially because of an unusual ability or quality
1. something (such as an interesting fact or event) that can be observed and studied and that typically is unusual or difficult to understand or explain fully.
2. someone or something that is very impressive or popular especially because of an unusual ability or quality
Tell about it, i wanna show you aurora phenomena...
An aurora is a natural light display in the sky (from the Latin word aurora, "sunrise" or the Roman goddess of dawn), predominantly seen in the high latitude (Arctic and Antarctic) regions. Auroras are caused by charged particles, mainly electrons and protons, entering the atmosphere from above causing ionisation and excitation of atmospheric constituents, and consequent optical emissions. Incident protons can also produce emissions as hydrogen atoms after gaining an electron from the atmosphere.
Visual forms & colours
Auroras take many different visual forms. The most distinctive and brightest are the curtain-like auroral arcs. They eventually fragment or ‘break-up’ into separate, and rapidly changing, often rayed features which may fill the whole sky. These are the ‘discrete’ auroras which are at times bright enough to read a newspaper by at night. The ‘diffuse’ aurora, on the other hand, is a relatively featureless glow sometimes close to the limit of visibility. It can be distinguished from moonlit clouds by the fact that stars can be seen undiminished through the glow. Diffuse auroras are often composed of patches whose brightness exhibits regular or near-regular pulsations. The pulsation period can be typically many seconds, so is not always obvious. Occasionally there is a fast, sub-second, flickering. A typical auroral display consists of these forms appearing in the above order throughout the night.
Auroras take many different visual forms. The most distinctive and brightest are the curtain-like auroral arcs. They eventually fragment or ‘break-up’ into separate, and rapidly changing, often rayed features which may fill the whole sky. These are the ‘discrete’ auroras which are at times bright enough to read a newspaper by at night. The ‘diffuse’ aurora, on the other hand, is a relatively featureless glow sometimes close to the limit of visibility. It can be distinguished from moonlit clouds by the fact that stars can be seen undiminished through the glow. Diffuse auroras are often composed of patches whose brightness exhibits regular or near-regular pulsations. The pulsation period can be typically many seconds, so is not always obvious. Occasionally there is a fast, sub-second, flickering. A typical auroral display consists of these forms appearing in the above order throughout the night.
Red: At the highest altitudes, excited atomic oxygen emits at 630.0 nm (red); low concentration of atoms and lower sensitivity of eyes at this wavelength make this colour visible only under more intense solar activity. The low amount of oxygen atoms and their gradually diminishing concentration is responsible for the faint appearance of the top parts of the "curtains".
Green: At lower altitudes the more frequent collisions suppress this mode and the 557.7 nm emission (green) dominates; fairly high concentration of atomic oxygen and higher eye sensitivity in green make green auroras the most common. The excited molecular nitrogen (atomic nitrogen being rare due to high stability of the N2 molecule) plays its role here as well, as it can transfer energy by collision to an oxygen atom, which then radiates it away at the green wavelength. (Red and green can also mix together to produce pink or yellow hues.) The rapid decrease of concentration of atomic oxygen below about 100 km is responsible for the abrupt-looking end of the lower edges of the curtains.
Yellow and pink are a mix of red and green or blue.
Blue: At yet lower altitudes atomic oxygen is, uncommon, and ionized molecular nitrogen takes over in producing visible light emission; it radiates at a large number of wavelengths in both red and blue parts of the spectrum, with 428 nm (blue) being dominant. Blue and purple emissions, typically at the lower edges of the "curtains", show up at the highest levels of solar activity.
Green: At lower altitudes the more frequent collisions suppress this mode and the 557.7 nm emission (green) dominates; fairly high concentration of atomic oxygen and higher eye sensitivity in green make green auroras the most common. The excited molecular nitrogen (atomic nitrogen being rare due to high stability of the N2 molecule) plays its role here as well, as it can transfer energy by collision to an oxygen atom, which then radiates it away at the green wavelength. (Red and green can also mix together to produce pink or yellow hues.) The rapid decrease of concentration of atomic oxygen below about 100 km is responsible for the abrupt-looking end of the lower edges of the curtains.
Yellow and pink are a mix of red and green or blue.
Blue: At yet lower altitudes atomic oxygen is, uncommon, and ionized molecular nitrogen takes over in producing visible light emission; it radiates at a large number of wavelengths in both red and blue parts of the spectrum, with 428 nm (blue) being dominant. Blue and purple emissions, typically at the lower edges of the "curtains", show up at the highest levels of solar activity.
Source : http://en.m.wikipedia.org/wiki/Aurora
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